Various types of clamping devices have been proposed and are practically used as clamping devices for fixing a workpiece (a clamping object) to a work fixing platform, such as a work pallet, etc.
For example, a clamping device that attracts and fixes a workpiece to a work fixing platform is disclosed in Ger. Laid-Open Patent Application DE-4020981-A1.
As shown in FIG. 19, in clamping device 200, a pull rod 202 is mounted to a clamping main body 201 so as to move freely vertically and protrude upward, and a tapered rod 202a, in which the horizontal cross-section becomes large toward upward, is formed at the upper end of the pull rod 202. A collet member 203 is externally fitted to the upper part of pull rod 202, and a collet 203a which is externally fitted to the tapered rod 202a and is elastically deformable to enlarge the diameter is provided in the collet member 203.
Moreover, an oil hydraulic cylinder 204 driving the pull rod 202 downward, a coil spring 205 energizing the pull rod 202 elastically upward and a plate spring 206 energizing the collet member 203 elastically upward are provided in clamping device 200.
The lower end of pull rod 202 is connected to a piston 204a of oil hydraulic cylinder 204, the piston 204a being elastically energized upward by the coil spring 205. The collet member 203 is supported from below by a collet supporting member 207, which is elastically energized upward by the plate spring 206.
When a workpiece W is fixed, if oil pressure is supplied to the oil hydraulic cylinder 204 in a state in which the tapered rod 202a and the collet 203a are inserted into a hole Wa formed in the workpiece W from below, the pull rod 202 is driven downward to lower the tapered rod 202a, at which time, the collet member 203 is elastically energized upward by the plate spring 206. Therefore the collet 203a is lowered only slightly, and is elastically deformed to the diameter enlargement side and engaged with the hole Wa, the workpiece W being attracted and fixed to a work receiving surface 201a of clamping main body 201.
In Japanese Laid-Open Patent Application H11-188551, the clamping device 200 and main constitution are basically the same, but a clamping device in which the pull rod is driven up/down by a reciprocating oil hydraulic cylinder is disclosed.
However, in the clamping device of the gazette, oil pressure must be continuously supplied to the oil hydraulic cylinder by oil pressure supply unit to fix a workpiece. Therefore, an oil pressure supply device must be provided in a work pallet to convey the workpiece with the work pallet in a state in which the workpiece is fixed to the work pallet by the clamping device. However, the conveying load of the work pallet increases if oil pressure supply unit is provided for each work pallet, and the equipment cost also rises.
The objects of the present invention are, in a clamping device, to fix simply and reliably a clamping object to a base, to simplify and miniaturize the structure to reduce manufacturing costs, to make it possible to fix a clamping object to a base by engaging to either the inner wall or the side wall of the hole of the clamping object, and to maintain the state of fixing the clamping object to the base without supplying oil pressure.